Flushing of third-phase contaminant from three-phase dispersion

ABSTRACT

Use of a vertical separating tank-hydraulic leg arrangement to continuously separate the light and heavy phases of a gravityseparable three-phase dispersion containing third-phase contaminants and to flush the contaminants at intervals.

[ Sept. 5, 1972 United States Patent Knepp m S W 4% m w m E s A H m mu TM m I MMN G m m H wmm LOB FCD M 1,534,145 4/1925Stedman......................210/84 [72] James KmPP Pmburgh, 2,342,9502/1944 Lovelady et al. ........210/84 x [73] Assignee: Aluminum Companyof America,

1,481,901 1/1924 Hapgood.................210/83X 2,808,933 10/1957Mobley........................210/83 Pittsburgh, Pa.

Dec. 28, 1970 [21] Appl. No.: 101,627

Pnmary Examiner-John Adee [22] Filed:

Attorney-Abram W. Hatcher [58] Field of heavy phases of agravity-separable three-phase dispersion containing third-phasecontaminants and to flush the contaminants at intervals.

Claims, 1 Drawing Figure l/V TERFACE BUILD UP NORMAL OPERA T/OIV MIDDLE'oF FL USH/NG START OF FLUSH/N6 END OF FLUSh'l/VG FLUSHING OFTHIRD-PHASE CONTAMINANT FROM THREE-PHASE DISPERSION BACKGROUND OF THEINVENTION 1 Field of the Invention This invention relates to process andequipment for accomplishing continuous gravity separation of athreephase system comprising a low-density liquid phase, for example,oil, an intermediate-density solid phase, for example, debris orcontaminants dispersed in liquid from the other two phases, and aheavy-density liquid phase, for example, water.

2. Description of the Prior Art Gravity separation of a two-phase liquiddispersion, for example, oil in water or water in oil, is known, Suchmay be accomplished in many types of tank designs providing for inflowof the two-phase dispersion, short holding time, and separate outflow ofthe two individual phases. The outflow of the heavy-liquid phase may bethrough a rising leg, that is, one which rises alongside the tank, ofsufficient hydrostatic height to balance the total hydrostatic head ofthe two phases inside the tank against a slightly smaller hydrostatichead of heavy-liquid phase in the rising leg. The height of the risingleg, the height of the overflow for the liqht-liquid phase, and thespecific gravities or densities of the two phases determine the heightof an interface which is established within the tank between the twophases. The design of separating tanks is usually emperical and, to alarger degree, depends on the gravity separating rate of the particulardispersion and the desired final purity of the separated phases. Theholding time generally ranges from a minimum of about minutes to amaximum of about 2 hours. Often encountered in the separation of twophases are solid contaminants or debris occurring in one or both phasesin substantial amounts. These form a third phase of intermediatespecific gravity. This phase formsby gravity in both directions, thatis, by spreading or growing upwardly and downwardly, at theaforementioned interface between the light and heavy-liquid phases.

SUMMARY OF THE INVENTION In its broader aspects, my invention involvesthe flushing of a solid-contaminants phase from a dispersion made up oflight-liquid, heavy-liquid and solidcontaminant phases. The flushing maybe accomplished at intervals either manually or automatically. It isbrought about by employing a tank which is of a greater verticaldimension, that is, height, than its largest measurement in a horizontaldirection, for example, diameter or length. I will refer to thisparticular type of tank hereinafter as a vertical separating tank.Flushing may be facilitated according to my invention by employing arestricted area in the lowermost or bottom portion of the verticalseparating tank, for example, a substantially funnel-shaped area, sothat the interface between the phase of light and heavy liquids wherethe solid contaminants collect or form in an intermediate zone or phasewhich also contains some of the heavy and light liquids is held in thisrestricted bottom area of the tank.

According to my invention, flushing of the accumulated interfacecontaminant or intermediate phase is accomplished either manually orautomatically by decreasing the hydrostatic support capacity of a risingheavy-liquid, for example, water, leg hereinafter referred to as therising water leg, or simply water leg, or just leg, which exits from thebottom of the tank, for example, a. leg which leaves the above-mentionedfunnel-shaped portion in a U-shaped path and rises alongside the tank toa controlled overflow point. As the interface begins to form, itcontinues to extend its area and volume both above and below theoriginal interface height or position. As the lowermost portion of thiscontinuously accumulating intermediate phase reaches the bottom of thetank, it finally reaches the point where it is automatically carriedover or washed into the rising water leg. Being of an intermediatespecific gravity, it then begins to reduce the specific gravity of therising water leg. This effect, in turn, reduces the hydrostaticsupporting head of the rising water leg for the body of liquid in thetank. This reduction of specific gravity and consequent reduction ofhydrostatic supporting head which begins the flushing may beaccomplished either manually, for example, by injecting a low-densityphase such as air into the rising water leg or, automatically, forexample, by lowering the overflow height or point of the rising waterleg, such as by opening a valve at a height lower than the standardoverflow on the leg. in other words, the height or volume of the waterleg is adjustable to control the level of the interface and formation ofintermediate contaminants phase. Reduction of the hydrostatic supportinghead of the water leg for the main tank accele rates the washing ofadditional intermediate specific gravity contaminant phase into thewater leg. This results in an increasingly more rapid flow of all of theaccumulated intermediate specific gravity or contaminant phase and thewashing, pushing or flushing of solid contaminants or debris out throughthe rising leg, which by this time has lost substantially all of itsprevious hydrostatic support. Flushing continues, with the light-liquid,or oil, phase now comprising most of the flow into the water leg, untilthe oil level in the tank reaches or extends to almost the level of therising water leg overflow. At this point, overflow stops, that is, afterthe contaminant phase has been pushed out through the rising legoverflow. The introduction of dispersion feed, which has been continuedthroughout the aforementioned operation, now again starts to separatethe heavy-liquid, or water, phase to the bottom of the tank andlight-liquid, or oil, phase to the top of the tank, with theintermediate contaminant phase once again forming by gravity between theheavy and light-liquid phases or layers. This automaticallyreestablishes or recommen ces the flushing cycle.

Representative dispersions which may be employed in the process of thisinvention include waste oil-water mixtures, grinding and machiningsoluble oils, rolling lubricant soluble oils, and mechanical lubricantsoluble oils.

According to my invention a flow of the heavy-density liquid promotesautomatic flushing. If the dispersion used does not have sufficient flowof heavy-density liquid because of its inherent capacity or the relativespecific gravities of the other phases, heavy-density liquid, or water,may be intentionally injected into the tank to provide sufficienthydrostatic support for the light-liquid, or oil, phase or layer and toassure the automatic re-establishment of the normal separation cycleafter discharge, flowing out or flushing of the intermediate contaminantphase.

According to my invention, the preferred way of supplying thethree-phase dispersion feed to the vertical separating tank is bygravity. However, a low-shear pump of the like may be used. Theinterface is preferably held below the feed level, that is, below thepoint of introduction of the dispersion to the tank, to preventpercolation of the oil phase through the interface. Holding of theinterface below the feed level prevents dragging of excess debris orcontaminants with the oil. Positioning of the interface at the desiredlevel is accomplished by making the heavy-liquid, or water, legadjustable in height. In other words, the lower the overflow level oroutlet point in the heavyliquid, or water, leg, the lower will be theposition or level of the interface in the tank. I

Representative of the light-liquid phase of the dime phase system whichthe present invention is adapted to separate into components are oils,such as mineral oils, particularly those used in rolling, cutting,hydraulic and other such areas of industrial lubrication. Suchlightphase liquids useful according to the invention generally havespecific gravities of from about 0.75 to about 0.95 and viscosities offrom about 30 to about 500 SSU/ 100 F. REpresentative contaminants ofthe intermediate phase include metallic fines, invert emulsion, soapsand other such debris. These form in an intermediate specific gravityphase at the interface between the light and heavy liquids which is ofhigher specific gravity than that of the lower, or light-phase, liquidwhich goes to the top, or forms the top layer, in the tank, that is,heavier than the representative 0.75 to 0.95 specific gravity, but, forthe most part, lighter than the specific gravity of the heavy liquidthat goes to the bottom, or forms the bottom layer, in the tank. Theheavy-liquid and light-liquid phases may be made up of liquids otherthan water and oil, for example, hydrocarbon solvents, or the like, oreven alcohols, or the like, provided they are sufficiently heavier thanor lighter than the other component of the dispersion introduced to thetank to be capable of separation into layers by gravity. For example,the heavy liquid may be water relatively free of oil and contaminant, ora form of stable emulsion, if the oil that is being separated is anunstable or unemulsified oil.

By the tank being required to be higher in a vertical direction than itis long or wide in a horizontal direction, it is restricted incross-section area. Preferably it is designed so as to have a portionnear the bottom of smaller diameter or length, for example, afunnel-shaped section, to facilitate formation of the interface areasufficiently low in the tank for the volume of contaminants andinterface debris to accumulate to a height, from top to bottom,sufficient to permit flushing according to the invention.

The dispersion treated according to the invention must be one which issufficiently unstable for the oil and water components to be separatedby gravity. For example, a broken emulsion may be used.

According t9 may invention there is a preferred relationship between theheights of phases and overflow and the specific gravities of the variousphases, assumthrough the pipes or the like to be negligible, viz.,

H2: L L ZH B" PH PL pL is the specific gravity of the light phase, pHthe specific gravity of the heavy phase, H, the height of the verticalseparating tank to overflow point or upper limit of light-liquid phase,H, the height from the interface or point from which the intermediatecontaminant phase forms thereabove and therebelow to the bottom of thetank and H, the height of the leg for heavy liquid to point of overflow,or exit opening or outlet, at which contaminants flow out. It isconvenient in designing the tank to relate the dwell time of the lightphase to the diameters and heights of various portions of the system asfollows:

(Dwell Time) L=4Wdrate)L D is the diameter or greatest horizontalmeasurement of the tank, usually the length, unless the length and widthare substantially equal, in this equation, and L represents the lightphase. The feed rate is indicated in cubic feet per minute and the dwelltime in minutes.

The following table gives representative design and operating ranges forvertical separating tanks which I have found useful according to theinvention. In addition to representative ranges for the flow velocitiesat various portions of the tank, representative heights involved andrepresentative diameters which I have found useful according to theinvention, a specific example of a preferred embodiment is given in thetable in which the various parameters are at optimum valves. in thetable, V, is the flow velocity of the entering feed, V, the flowvelocity of the light, or oil, phase moving upward in the tank, V, thevelocity of the downwardmoving heavy, or water, phase, V, the velocityof the liquid moving upward in the water leg to the overflow point, D,the diameter of the entering dispersion feed stream orifice, D, thediameter of the larger upper portion of the generally funnel-shapedtank, such as that depicted in the drawing, which s 131 is hereinbelow,D, the diameter of the lower, or restricted-area, portion of the tankand D, the diameter of the necked heavier liquid, or water, phaseoverflow leg.

TABLE Design and Operating Ranges Flow Velocities Example* V, lO-l 5ft/min 14.2 ft/min V, 0.05-0.2 ft/min .14 ft/min V 0.2-1.5 ft/min .76ft/min V 5-50 ft/min 13.3 ft/min Heights H, 8-16 ft 11 ft H, 2-4 ft 3 ftH, Dependent on H, and

H, 9.6 ft Diameters D, 6-10 in 10 in D, 3-7 ft 3 ft D, 1.5-3 ft 3 ft D,4-8 in 6 in Phase Contaminants Water in oil overflow 0-l0% .l% Oil inwater overflow l-l5% [0% Dwell Time l-2 hours Flow Rate of 40 gpm oil/20gpm water For a better understanding of the invention, reference willnow be made to the drawing which forms a part hereof.

The drawing is a schematic representation of a vertical separating tankuseful according to the invention with an adjacent hydraulic legconnected thereto for use in flushing or drainage of layers atintervals. The drawing shows the various steps of an operating sequenceaccording to the invention from the beginning through the end of a firstor illustrative cycle. In the drawing, the various steps of the processof the invention are shown, from build-up of an intermediate solidcontaminant, or debris, phase or layer and the start of flushing untilthe re-establishment of the interface and intermediate layer before thebeginning of a second flushing cycle. A dispersion or emulsioncontaining oil 10, water 12, and solid or particulate contaminants orimpurities 14, such as metallic fines, invert emulsion, soaps, or thelike, is introduced continuously to vertical separating tank 16 via line18. With continued introduction of the emulsion, the intermediate solidcontaminants (solids plus oil plus water) layer 20 begins to build upbetween the heavier, or lower, water layer 22 and the lighter, or upperoil, layer 24. During normal or standard operation, the oil, after buildup, overflows at 26. The water layer flows out via hydraulic leg 28 at30, and when the solid contaminants of density intermediate that ofwater and oil 32 are carried into rising water leg 28 as the specificgravity and hydrostatic supporting head of the rising water leg 28 arereduced, the solid contaminants are also washed out from the risingwater leg 28 at 30, after flushing of the heavy, or water, layertherethrough. Then a new cycle begins, with new oil, water and solidcontaminant layers forming and flushing again taking place. Before a newlower water layer forms, a small amount of oil may pass out at 30.

DESCRIPTION OF THE PREFERRED EMBODIMENT The following example isillustrative of the invention. In this example the items H H H V V andV, have the same meaning and significance as in the table usedhereinabove.

A sample of industrial waste oil containing approximately 24 percentoil, 2 percent interface debris, and 74 percent water was used todemonstrate use of a vertical separating tank according to theinvention. A tank having a total height of 17 feet and a diameter of 3inches ID (internal diameter) was used in this example. The followingdata were obtained from three individual or separate trials.

Trial 1 Trial 2 Trial 3 Tank Temperature F 128 I20 I27 Feed to Tank:

Method pump gravity gravity oil 75 24 25 interface 2 l I water 23 75 74Specific Gravity .890 .965 .965

Height (H,) in. 158.8 158.8 158.8 "'5 water 0.5 16 2.5

Specific Gravity .852 .874 .857

Velocity (V,) ft/min .213 .208 .044

Water Overflow Height (11,) in. 149.5 149.5 149.5

% Oil 3 0.5 0.5 Specific Gravity .999 .997 .999 Velocity (V ft/min 0.1541.52 0.86 Velocity (V ft/min 1.6 16.0 9.05 Interface Height (11,) in.

Visual 30 I6 34 Calculated 95.2 82.8 93.6 Specific Gravity .982 .982.982

As the separation process or cycle continued, a third intermediatespecific gravity phase (alternatively referred to as interface debris)accumulated in the area of a visual interface height. The intermediatephase increased in accumulated volume, extending in height from severalinches above the tank bottom of a tank, such as depicted in the drawingand described hereinabove in connection with the table illustratingcertain preferred design features thereof, to a height of approximately40 inches. As the lower portion of the intermediate phase was carriedover or washed into the water leg, a reduction of the specific gravityin the supporting water leg occurred. The reduced hydrostatic support ofthe water leg caused the main separating tank to flush the remainingaccumulated intermediate phase through the water leg at a rapid flowuntil the oil level in the tank was nearly equal to the overflow heightof the water leg. At that point the flow of oil from the water overflowstopped, the water phase of the feed separated to the tank bottom, andthe normal operating separation cycle was re-established and continued.

While the invention has been described in terms of preferredembodiments, the claims appended hereto are intended to encompass allembodiments which fall within the spirit of the invention.

Having thus described my invention and certain embodiments thereof, 1claim:

1. In a process comprising gravity separation of two liquid phases of adispersion made up of a light-liquid phase an a heavy-liquid phase, thelight-liquid phase being of a lower specific gravity than theheavy-liquid phase, by introducing a dispersion of the two phases into asettling tank which has a leg leaving the bottom thereof and risingalongside same, separating the two phases by gravity into an upper layercomprising the light liquid and a lower layer comprising the heavyliquid, and forming by gravity an intermediate phase containing solidsbetween the two layers in the tank, the steps which comprise prior toflushing accumulating the intermediate phase containing solids in alower restricted-area portion of the tank and flushing said intermediatephase containing solids from said tank by automatically decreasing thehydrostatic support capacity of said leg.

2. The steps of claim 1 wherein the decreasing of the hydrostaticsupport capacity of the leg is accomplished by positioning an overflowsufficiently low in the leg for the flushing to be accomplishedautomatically.

3. The steps of claim 1 wherein prior to flushing said intermediatephase is caused to gradually accumulate in depth by growing upward anddownward from an original interface which forms by gravity between theheavy-liquid phase and the light-liquid phase until it is pushed overinto the leg, and, as a result, the specific gravity of the rising waterleg is reduced, thereby causing said decreasing of the hydrostaticsupporting capacity of the leg and accelerating the washing of saidintermediate phase into said leg, the accumulated intermediate phasebeing flowed at an increasingly more rapid rate through the leg and outof the system until the lighter phase comprises substantially all of theflow into the leg and reaches a height in the leg at which it overflows,and thereafter the light-liquid, heavy-liquid and intermediate phases inthe tank are automatically reestablished, whereupon the heavy-liquidphase once again begins to form in the bottom of the tank.

4. A process for separation of contaminants from a three-phasedispersion which comprises introducing a dispersion comprising alight-liquid phase, a heavyliquid phase and solid contaminants into aseparating tank of a vertical dimension which is greater than ahorizontal dimension thereof, permitting the dispersion to form bygravity into three phases comprising an upper light-liquid phase, alower heavy-liquid phase and an intermediate phase between said upper anlower phases, said intermediate phase comprising solid contaminantsdispersed in a mixture of said heavy liquid and said light liquid, andflushing said intermediate phase from said tank through an outlet in ahydrostatic leg which leaves the bottom of said tank and makes asubstantially U-shaped turn to continue upward alongside said tank bydecreasing the hydrostatic support capacity of said leg, said tankcontaining a portion in the bottom thereof of lesser horizontaldimension than the remainder of the tank whereby the pushing of theheavy-liquid phase followed by the intermediate phase containing solidcontaminants is facilitated.

5. A process for separation of contaminants from a three-phasedispersion which comprises introducing a dispersion comprising alight-liquid phase, a heavyliquid phase and solid contaminants into aseparating tank of a vertical dimension which is greater than ahorizontal dimension thereof, permitting the dispersion to form bygravity into three phases comprising an upper light-liquid phase, alower heavy-liquid phase and an intermediate phase between said upperand lower phases, said intermediate phase comprising solid contaminantsdispersed in a mixture of said heavy liquid and said light liquid, andflushing said intermediate phase from said tank through an outlet in ahydrostatic leg which leaves the bottom of said tank and makes asubstantially U-shaped turn to continue upward alongside said tank bydecreasing the hydrostatic support capacity of said leg, said tankcontaining a portion in the bottom thereof of lesser horizontaldimension than the remainder of the tank whereby the pushing of theheavy-liquid phase followed by the intermediate phase containing solidcontaminants is facilitated, the height of the intermediate phase insaid tank, as measured from an interface which forms between thelight-liquid phase and the heavy-liquid phase and which interface growsupward and downward from the point of formation thereof to the bottom ofsaid tank at the point at which the leg leaves the tank being controlledso as to be substantially equal to a quantity which is the differencebetween the product of the height of said leg to said outlet and thespecific gravity of the heavy-liquid phase and the product of theoverall height of said tank to an overflow point of the light-liquidphase therein and the specific gravity of the light-liquid phase, saidquantity being divided by a quantity which is the difference between thespecific gravity of the heavy-liquid phase and the specific gravity ofthe light-liquid phase.

2. The steps of claim 1 wherein the decreasing of the hydrostaticsupport capacity of the leg is accomplished by positioning an overflowsufficiently low in the leg for the flushing to be accomplishedautomatically.
 3. The steps of claim 1 wherein prior to flushing saidintermediate phase is caused to gradually accumulate in depth by growingupward and downward from an original interface which forms by gravitybetween the heavy-liquid phase and the light-liquid phase until it ispushed over into the leg, and, as a result, the specific gravity of therising water leg is reduced, thereby causing said decreasing of thehydrostatic supporting capacity of the leg and accelerating the washingof said intermediate phase into said leg, the accumulated intermediatephase being flowed at an increasingly more rapid rate through the legand out of the system until the lighter phase comprises substantiallyall of the flow into the leg and reaches a height in the leg at which itoverflows, and thereafter the light-liquid, heavy-liquid andintermediate phases in the tank are automatically re-established,whereupon the heavy-liquid phase once again begins to form in the bottomof the tank.
 4. A process for separation of contaminants from athree-phase dispersion which comprises introducing a dispersioncomprising a light-liquid phase, a heavy-liquid phase and solidcontaminants into a separating tank of a vertical dimension which isgreater than a horizontal dimension thereof, permitting the dispersionto form by gravity into three phases comprising an upper light-liquidphase, a lower heavy-liquid phase and an intermediate phase between saidupper an lower phases, said intermediate phase comprising solidcontaminants dispersed in a mixture of said heavy liquid and said lightliquid, and flushing said intermediate phase from said tank through anoutlet in a hydrostatic leg which leaves the bottom of said tank andmakes a substantially U-shaped turn to continue upward alongside saidtank by decreasing the hydrostatic support capacity of said leg, saidtank containing a portion in the bottom thereof of lesser horizontaldimension than the remainder of the tank whereby the pushing of theheavy-liquid phase followed by the intermediate phase containing solidcontaminants is facilitated.
 5. A process for separation of contaminantsfrom a three-phase dispersion which comprises introducing a dispersioncomprising a light-liquid phase, a heavy-liquid phase and solidcontaminants into a separating tank of a vertical dimension which isgreater than a horizontal dimension thereof, permitting the dispersionto form by gravity into three phases comprising an upper light-liquidphase, a lower heavy-liquid phase and an intermediate phase between saidupper and lower phases, said intermediate phase comprising solidcontaminants dispersed in a mixture of said heavy liquid and said lightliquid, and flushing said intermediate phase from said tank through anoutlet in a hydrostatic leg which leaves the bottom of said tank andmakes a substantially U-shaped turn to continue upward alongside saidtank by decreasing the hydrostatic support capacity of said leg, saidtank containing a portion in the bottom thereof of lesser horizontaldimension than the remainder of the tank whereby the pushing of theheavy-liquid phase followed by the intermediate phase containing solidcontaminants is facilitated, the height of the intermediate phase insaid tank, as measured from an interface which forms between thelight-liquid phase and the heavy-liquid phase and which interface growsupward and downward from the point of formation thereof to the bottom ofsaid tank at the point at which the leg leaves the tank being controlledso as to be substantially equal to a quantity which is the differencebetween the product of the height of said leg to said outlet and thespecific gravity of the heavy-liquid phase and the product of theoverall height of said tank to an overflow point of the light-liquidphase therein and the specific gravity of the light-liquid phase, saidquantity being divided by a quantity which is the difference between thespecific gravity of the heavy-liquid phase and the specific gravity ofthe light-liquid phase.